Marine trace fossils and microbially induced sedimentary structures of the Miocene- Pliocene Río Negro Formation.

CARMONA, NOELIA B.; PONCE, JUAN JOSE; WETZEL, ANDREAS; BOURNOD, CONSTANZA N.; CUADRADO DIANA G.

La Pampa

Congreso; SECOND LATIN AMERICAN SYMPOSIUM ON ICHNOLOGY; 2013

International Ichnological Association

The upper Miocene to lower Pliocene Río Negro Formation (Andreis, 1965)extensively crops out in the northern region of Patagonia, Argentina, in particular along seacliffs and river-cut valleys (Fig. 1). Zavala et al. (2000) have distinguished threeunconformity-bounded members within this formation (Fig. 1B, 2A). The lower memberconsists mostly of medium- to coarse-grained sandstones and mudstones formed in aneolian setting, characterized by large dunes and dry or wet interdunes. The middle membercomprises sandstones with abundant bioclasts and dark gray mudstone intervals depositedin a shallow-marine environment; this member records a complete transgressive?regressivecycle (Zavala and Freije, 2000; Zavala et al., 2000). The upper member is composed ofsandstones that formed in an eolian setting at the lower part (similar to those recognized inthe lower member), paleosols and tuff levels toward the top of the member. The absence oftectonic structures in the studied formation suggests a period of relative tectonicquiescence, at least for late Neogene times (Zavala and Freije, 2001).